As mobile devices have been increasingly developed, and the demand of such mobile devices has increased, the demand of secondary batteries has also sharply increased as an energy source for the mobile devices. Among them is a lithium secondary battery having high energy density and high discharge voltage, on which much research has been carried out and which is now commercialized and widely used.
Based on its external shape, the lithium secondary battery may be generally classified as a cylindrical battery, a prismatic battery, or a pouch-shaped battery.
Based on its electrolyte, the lithium secondary battery may be classified as a lithium-ion battery or a lithium-ion polymer battery. As the mobile devices have been miniaturized, the demand of the rectangular battery and the pouch-shaped battery, which have a relatively small thickness, has increased.
Furthermore, based on how the secondary battery is mounted to a case, a battery pack may be generally classified as a hard battery pack or an inner battery pack.
The hard battery pack forms a part of the external appearance of an external device, to which the hard battery pack is mounted. Consequently, the hard battery pack has an advantage in that the hard battery pack can be easily mounted to the external device when in use. However, it is required to design a case based on kinds of corresponding external devices while a battery cell is mounted in the case. As a result, the manufacturing costs of the hard battery pack are high, and, furthermore, the hard battery pack has low compatibility with the external devices.
On the other hand, the inner battery pack is mounted in an external device, and is then hidden by a cover, which forms a part of the external device. As a result, although it is relatively troublesome to mount the inner battery pack in the external device, the inner battery pack has advantages in that it is easy to design the inner battery pack, the manufacturing costs of the inner battery pack are low, and the inner battery pack has high compatibility with the external devices.
The prismatic battery or the pouch-shaped battery is widely used as a battery cell, which is a main body of the inner battery pack. The prismatic battery is a battery having an electrode assembly mounted in a battery container, which is made of aluminum or stainless steel. The pouch-shaped battery is a battery having an electrode assembly mounted in a pouch-shaped battery case, which is made of an aluminum laminate sheet. Recently, the demand of the pouch-shaped battery has increased because the weight of the pouch-shaped battery is small, the costs of the pouch-shaped battery are low, and the pouch-shaped battery can be easily deformed depending upon the capacity and output of the battery pack.
FIGS. 1 and 2 are a perspective view and an exploded perspective view respectively illustrating a conventional inner battery pack including a pouch-shaped battery cell.
Referring to these drawings, the battery pack 10 includes a battery cell 20, in which an electrode assembly including cathodes, anodes, and separators is mounted together with an electrolyte in a sealed state, a pack case body 30 having an inner space for receiving the battery cell 20, and a top cover 40 joined to the top of the pack case body 30, in which the battery cell 20 is received, for sealing the battery cell 20. Between the pack case body 30 and the battery cell 20 and between the top cover 40 and the battery cell 20 are attached double-sided adhesive tapes 50, respectively.
The battery pack cases 30 and 40 supplement the small mechanical strength of the pouch-shaped battery cell 20; however, the battery pack cases 30 and 40 restrict the size of the battery cell 20, with the result that the total capacity of the battery pack is reduced. Furthermore, the pack case body 30 and the top cover 40 are joined to each other by an ultrasonic welding method. Consequently, it is required that the pack case body 30 and the top cover 40 be manufactured with a specific thickness to form the joint interface between the pack case body 30 and the top cover 40, at which the pack case body 30 and the top cover 40 are joined to each other, with the result that the volume of the battery pack is increased.
Recently, therefore, there has been increasingly used a frame-shaped pack case for covering only the side of the battery cell, instead of a box-shaped pack case for covering all the outer surface of the battery cell, to minimize the volume of the battery pack and to effectively supplement the strength of the battery cell. For example, Japanese Patent Application Publication No. 2004-0094633 discloses a battery pack including an integration type pouch-shaped case, which has a first region at which a receiving part for receiving an electrode assembly is formed, a second region extending from the first region such that the second region covers one surface, which is exposed to the outside, of the electrode assembly, and a third region extending from the second region, such that the third region covers the first region and one end of the third region is brought into contact with the second region, and a frame member mounted to the battery cell such that the frame member covers the outer surface of the receiving part before the first region is covered by the third region. In addition, the publication discloses a separation type pouch-shaped case including a first packing member having a receiving part for receiving an electrode assembly and a second packing member having a first region for sealing the first packing member while covering one surface, which is exposed to the outside, of the electrode assembly and a second region extending from the first region such that the second region covers the outer surface of the first packing member.
In the battery pack with the above-stated construction, however, the outermost surface of the battery pack is not covered by an additional sheathing member, with the result that the bent parts and the joint parts of the packing members are exposed to the outside, and therefore, the surface of the battery pack is not smooth. This problem may serve as a main cause of inflicting injury on an engineer or a user and to threaten the security of the engineer or the user during the manufacture or use of the battery pack. In addition, the external appearance of the battery cell, mounted in the battery pack, is maintained by the frame member, and the strength of the battery cell is supplemented by the frame member; however, the top and bottom of the battery cell, which is not protected by the frame member, are covered by only the packing members, which are mechanically weak. Consequently, it is not possible to achieve a desired strength.
On the other hand, various kinds of combustible materials are contained in the lithium secondary battery. As a result, the lithium secondary battery may be heated or explode due to the overcharge of the battery, the overcurrent in the battery, or other physical external impacts. That is, the safety of the lithium secondary battery is very low. Consequently, the lithium secondary battery includes a protection circuit module (PCM), which is connected to the battery cell for effectively controlling an abnormal state of the battery, such as the overcharge of the battery.
Generally, the PCM is connected to the battery cell via conductive nickel plates by welding or soldering. Specifically, the nickel plates are joined to electrode tabs of the PCM by welding or soldering, and then the nickel plates are joined to electrode terminals of the battery cell by welding or soldering. In this way, the PCM is connected to the battery cell to manufacture a battery pack.
In this case, the welding or soldering process must be carried out several times to manufacture the battery pack. The welding or soldering process must be carried out very precisely due to the small structure of the secondary battery, and therefore, a possibility of battery defect is increased. Furthermore, the addition of the above-described process increases the manufacturing costs of products.
Consequently, there is a high necessity for a technology that is capable of fundamentally supplementing the strength of the battery pack, including the pouch-shaped battery cell, effectively increasing the capacity of the battery pack, and easily assembling the battery pack, thereby lowering the manufacturing costs of the battery pack.